19 Nov Re-Engineer Case Wear Rings for CCW Pump
During the dismantling process of a client’s CCW pump we found that the DE bearing had collapsed and because of this the rotor had dropped from its normal running position. As the rotating element dropped the clearances between the impeller wear ring and case wear ring closed at the bottom of the pump and at the top of the pump opened.
During the FARO inspection a line was drawn through the centre of the pump casings. From this we could determine that the two bearing carriers were out of parallel by 0.4mm.
Failure of the DE bearing we believe is down two 2 major factors.
- The bearing carrier being out off parallel to NDE by approximately 0.40mm.
- The pump shaft shoulder that the bearing ID locates to was on 0.15mm step, the bearing has an R2 on its inner race so this would allow for the bearing to easily be cocked over, its was also not retained on its outer race which makes it even more vulnerable to this.
The case wear rings were 40% – 70% above the manufactures suggested clearances, causing excessive leakage and producing a reduction in efficiency. This hydraulic loss affects the performance and efficiency as demin water moves from the high-pressure side to the low-pressure side and this in turn causing smaller flow. It may also reduce hydraulic damping of the rotating element thus increasing possible vibration and shaft deflection.
Refurbishment of the worn case wear rings was considered but due to their design this was not a possibility.
Case Wear Ring showing excessive clearance.
Worn Case Wear Ring DE
Close up of damage to NDE Case Wear RingFirstly we needed to create drawings from the old parts, bearing in mind these parts were worn, so paying important attention to critical fits and tolerances on the copied parts, if these were wrong they could lead to individual part or pump failures.
As mentioned previously making sure the clearances between the impeller wear ring and case wear ring were correct as to not cause recirculation.
Secondly making material selection, for the case wear rings LG1Bronze was chosen as it’s a durable, good wearing bronze that is commonly used in pump bodies, elbows, pipes and plain bearings bushes. It has great corrosion resistance and combined with suitable lubrication has exceptional load bearing potentials
Once the drawings and material selection were complete we were able to Re-Engineer the two new case wear rings.
Machining drawing of the Re-Engineered Case Wear RingsDuring and after machining, the Re-Engineered parts underwent stringent quality control procedures making sure they were well within the critical fits and tolerances.
New Case wear rings were fitted to the CCW pump, clearances were verified guaranteeing hydraulic losses would be kept within the manufactures tolerances and rebuild was completed.
The pump was commissioned and is running well with no issues.
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Whilst in service on a plant in SA. This fluid coupling is situated between a Siemans three-phase motor and a 6”/8” 10 stage boiler feed pump.
The unit was suffering from a large amount of vibration and was unable to adjust its speed.
The Re-Engineer of Case Wear Rings for Horizontal Split Case single Stage Double Suction Pump (CCW).
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